A motor is a device that is used in many applications, such as various home electric appliances and automobiles, and, in these years, there have been increasing demands for motors having a higher level regarding the reduction in size and increase in output. Due to the tendency, a motor rotation number increases, and a motor, which can adapt to the increase and exert long operation life, is requested.
Examples of stopping of a motor caused by the end of life time include stopping due to mechanical abrasion generated between a commutator and a brush that are constituent parts of the motor. In the phenomenon, a material of a commutator moves and adheres to a brush as a result of abrasion caused by sliding in a motor drive process, which moves and adheres again to the commutator to generate coarse abrasion particles in the process. Then, the abrasion particles accumulate in a slit of the commutator, and the commutator short-circuits to stop the motor. When the mechanism is considered, an effort for making operation life of a motor longer includes improvement of abrasion resistance properties of sliding contact materials constituting these parts.
As a sliding contact material applied to a motor, etc., an Ag-based alloy is well known, in consideration of electroconductivity in addition to abrasion resistance. For example, there are known an Ag—Cu alloy in which Ag is alloyed with Cu, an Ag—Cu—Zn alloy and an Ag—Cu—Zn—Mg alloy, etc. in which Zn, and additionally Mg is alloyed.